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DNR confirms zebra mussels in lower Otter Tail River

It’s probably just a matter of time now before zebra mussels make their ugly appearance along the Grand Forks stretch of the Red River and points downstream.

The presence of larval-stage zebra mussels, or veligers, was confirmed in 2010 at the source of the Red River in Wahpeton-Breckenridge after the invasive species was found the previous year in Pelican Lake farther upstream in the Red River watershed.

Since then, there haven’t been any confirmed reports of adult zebra mussels in the Red. But this week, the Minnesota Department of Natural Resources, confirmed the presence of adult zebra mussels in the Otter Tail River downstream from the Orwell Dam. DNR officials said low water levels in the river revealed zebra mussels of various sizes attached to rocks and debris.

As a result, lower reaches of the Otter Tail River from the confluence of the Pelican River downstream to the Bois De Sioux River confluence — where the Red River begins — will be designated as infested waters.

The DNR also will designate Lake Miltona and Lake Ida as infested waters, the latter for precautionary reasons because it is the next lake downstream from Miltona.

There was at least a glimmer of good news, though, in Lake Irene in Douglas County and Rose Lake in Otter Tail County, where DNR officials didn’t find any larval zebra mussels after an eradication effort to remove juvenile zebra mussels that had been found in small, localized areas of both lakes.

The DNR used copper sulfate in an attempt to eradicate the mussels and completed fieldwork to evaluate the efforts this past week.

“We did not find any veligers in our water samples or large zebra mussels during our scuba searches this summer,” said Nathan Olson, DNR invasive species specialist in Fergus Falls. “However, during our fall searches, we did find adult zebra mussels in both lakes.”

In a news release, Olson said that because monitoring efforts did not produce any veligers or juvenile zebra mussels, the DNR cannot confirm that zebra mussels have reproduced in either lake. The recent find of adult mussels means that despite early detection and a rapid DNR response, efforts to kill the zebra mussels in these lakes were not successful.

DNR staff will continue to monitor these lakes next year to evaluate the zebra mussel populations.

More information about aquatic invasive species is available on DNR website at www.mndnr.gov/ais.